You know that when you use a lock screen, it's often quite easy to know your combination by simply looking at the grease traces of your display? Well now there's finally an app against that. And it's called SmearSafe. Apparently, it was developed by people connected to the University Stuttgart. I've checked the whois entries and saw that the domain hcilab.org is really registered to the name of the professor of the University Suttgart. Further than that, I can't really validate their identity. But it appears ok.

The app works by changing around the image in a way that the way you have to move your fingers is different each time. I.e. it turns, distorts, moves and mirrors the image in different ways. This way the smears get mixed up and it's pretty much impossible for someone who sees your hand movements to guess your login. Of course, it may also require a bit more brain power on your side.

Let me know how it goes for you! Note: I had to set it up twice before it actually started to work on my phone. And it will request admin priviledges to be able to unlock your screen without being set to root.